58 
ALL SMALL BotroM-ANIMALS, HAVANA TO GRAND IsLtanp*, 1915 anp 1920 
1, Average numbers per square yard 
Channel 4-7-ft. zone 1-3-ft. zone 
1915 1920 | 1915 1920 | 1915 1920 
Viviparidae and 
Pleuroceridae 6 10 73 9 99 104 
Sphaeriidae 6 2 84 12 89 12 
Amnicolidae, Val- 
vatidae, etc. 0 0 4 0 2 0 
Chironomidae trace 36 2 170 6 244 
Oligochaeta 0.5. 2 9 33 0 24 
Other insects, worms, 
Crustacea, etc. 3 78 20 27 12 429 
Grand total 15 128 192 251 208 813 
| 
* To 1 mile below head of Grand Island in 1920; to head of Grand Island in 1915. 
2. Average pounds per acre 
Channel 4-7-ft. zone . 1-3-ft. zone 
1915 1920 | 1915 1920 | 1915 1920 
+ 1° | 
Viviparidae and E 
Pleuroceridae 16 9 | 235 aht 386 312 
} 
Sphaeriidae 3 1 42 6 44 6 
Amnicolidae, Val- 
vatidae, ete. 0 0 0.1 0 (pal 0 
Total snails 19 10 277 ity 430 318 
Chironomidae trace 6 0.3 45 1 122 
Oligochaeta 0.1 trace 0.3 1 0 i! 
Other insects, worms, 
Crustacea, etc. 3 145) 5 26 4 85 
Grand total 22 30 | 283 89 | 435 526 
1 
Per cent. snails 86.3 33.3| 97.8 OR 9828) 60.4 
